How can I change the format

See more:

C#

Hello everyone, I have a program that records the times, the code writes the start time in the Start text field and the end time in the End text field, this would be saved as a list in the Observable Collection.
then the list is added to the datagrid table then the whole is written to a text file.

Now I could transform the format in text fields as desired and I could also transform everything in text files by overwriting the To string method in Timer class and returning it in the desired format as a string.

the problem is how can I transform the formats in datagrid?

the difference happens here:

I don't know if ObservableCollection would be a good choice and if you can get to every single element in this kind of list and change the format?

instead of:

00: 00: 00.000000

these will:

00:00:00

What I have tried:

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Collections.Specialized;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Forms;
using System.Drawing;
using System.Linq;
using System.IO;

namespace TimeRecorderPro
{
    /// <summary>
    /// Interaktionslogik für MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public DateTime startTime;
        public DateTime endTime;
        public Timer _currentTimer;
        public DateTime Dauer;

        System.Windows.Forms.NotifyIcon notifyIcon = new System.Windows.Forms.NotifyIcon();

        public void SetinTab()
        {
            Timers.Add(_currentTimer);
            btnStart.Content = "Start";
        }
        void Löschen()
        {
            txtStart.Text = "";
            txtEnde.Text = "";
        }
        public void BemerkungEinfuegen(string str)
        {
            _currentTimer.Bemerkung = str;
        }
        private ObservableCollection<Timer> Timers;
        public MainWindow()
        {
            InitializeComponent();
            Timers = new ObservableCollection<Timer>{};
            lstNames.ItemsSource = Timers;
            this.ShowInTaskbar = false;
            
            notifyIcon.Icon = new System.Drawing.Icon(@"C:\Users\mmohammadi\source\repos\WPF Proj\TimeRecorderPro\TimeRecorderPro\bin\Debug\66164.ico");
            
            notifyIcon.MouseClick += notifyIcon_MouseDoubleClick;
        }
        private void btnStart_Click(object sender, RoutedEventArgs e)
        {
            if ((string)btnStart.Content == "Start")
            {
                _currentTimer = new Timer();
                txtStart.Text = _currentTimer.Start.ToString("T");
                btnStart.Content = "Ende";
            }
            else
            {
                _currentTimer.Ende = DateTime.Now;
                txtEnde.Text = _currentTimer.Ende.ToString("T");

                _currentTimer.Dauer = _currentTimer.Ende - _currentTimer.Start;

                txtEnde.Text = _currentTimer.Ende.ToString("T");

                Bemerkung bemerkungsdialog = new Bemerkung();
                bemerkungsdialog.Owner = this;
                bemerkungsdialog.WindowStartupLocation = WindowStartupLocation.CenterOwner;
                bemerkungsdialog.ShowDialog();

                SetinTab();
                Löschen();
            }
        }
        private void Window_Closing(object sender, System.ComponentModel.CancelEventArgs e)
        {
            MessageBoxResult mbresult = System.Windows.MessageBox.Show("Möchten Das Programm wirklich beenden?", "Programm beenden", MessageBoxButton.YesNo);

            if (MessageBoxResult.No == mbresult)
            {
                e.Cancel = false;

            }

            e.Cancel = true;
            this.Visibility = Visibility.Hidden;

            string testtext = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments) + "/Zeitbuchung_" + DateTime.Now.ToString("yyyyMMdd_HHmmss") + ".txt";

            var objWriter = new System.IO.StreamWriter(testtext);

            foreach (Timer timer in Timers)
            {
                objWriter.WriteLine(timer.ToString());
            }

            objWriter.Close();
            notifyIcon.Visible = true;
        }

        private void lstNames_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
        }

        private void Window_SizeChanged(object sender, SizeChangedEventArgs e)
        {
            if (this.WindowState == WindowState.Minimized)
            {
            }
        }

        private void notifyIcon_MouseDoubleClick(object sender, MouseEventArgs e)
        {
            this.WindowState = WindowState.Normal;
            notifyIcon.Visible = false;
            this.Show();
        }
    } 

    public class Timer
    {
        public Timer()
        {
            Start = DateTime.Now;
        }

        public DateTime Start { get; set; }
        public DateTime Ende { get; set; }
        public TimeSpan Dauer { get; set; }
        public string Bemerkung { get; set; }

        public override string ToString()
        {
            return "Start : " + Start.ToString("T") + " \nEnde  : " + Ende.ToString("T")
                   + "\nDauer : " + Dauer.TotalHours.ToString("0.00") + "\nBemerkung : " + Bemerkung.ToString();
        }
    }    
}